According to a speeding-up of a wireless communication, a high-efficiency transmission by digitization has recently been employed. Under these circumstances, in order to suppress the deterioration of a signal quality, a high linearity in a power amplifier is expected. Also, at the same time, in view of, for example, miniaturization or operating cost reduction of a device, the development of a power amplifier operating at a high power exchange efficiency is being carried out. In general, however, in the power amplifier, linearity and a power exchange rate are in a conflict relationship with each other.
Therefore, in order to achieve both the linearity and the power exchange efficiency, the power amplifier is operated in a non-linear region where the power exchange efficiency is high, and the linearity is maintained using a distortion compensation device that is configured to remove the non-linear distortion occurring at that time. As a distortion compensation system used in the distortion compensation device, there is, for example, a predistortion scheme (hereinafter, referred to as a “PD scheme”). The PD scheme is a technology that increases the linearity at the output of a power amplifier by providing an inverse characteristic of non-linear distortion of the power amplifier to a transmission signal in advance. In a distortion compensation device that employs the PD scheme, for example, a distortion compensation coefficient for performing distortion compensation is stored in a look-up table (LUT), and an address according to the power or the amplitude of an input signal input to a power amplifier is designated so as to read the distortion compensation coefficient from the LUT.
Here, it has been known that a phenomenon called a memory effect occurs in a power amplifier. The memory effect refers to a phenomenon in which an output signal according to an input signal of a power amplifier at a certain time point is influenced by a past input signal. When the memory effect of the power amplifier occurs, there is a concern that a distortion compensation performance may be deteriorated in the distortion compensation device that designates only an address according to the power or the amplitude of the input signal at the present time.
In contrast, there is suggested a technology in which an address according to a phase difference of input signals at different time points (hereinafter, referred to as a “phase difference address”) is generated in addition to an address according to a power or an amplitude of a signal at the present time, and an address is designated based on the phase difference address so as to read a distortion compensation coefficient from a LUT.
Related technologies are disclosed in, for example, Japanese Laid-open Patent Publication No. 2011-499429.